The present invention relates to a tool for drilling/routing of printed circuit board materials. By alloying the binder phase with Ru in combination with the use of fine grained Co-powder the properties have been improved.
Cemented carbide containing Ru as binder phase alone or in combination with the conventional Co and/or Ni is known in the art. For example, AT 268706 discloses a hard metal with Ru, Rh, Pd, Os, Ir, Pt and Re alone or in combination as binder phase. U.S. Pat. No. 4,574,011 discloses a hard metal composition for ornamental purposes with a binder phase of Co, Ni and Ru. GB 1309634 discloses a cutting tool with a Ru binder phase. GB 622041 discloses a hard metal composition a Co+Ru binder phase.
The routing of Printed Circuit Board materials requires a wide range of properties from the tool material in order for it to perform successfully. These include a hardness in excess of 2000 HV, a resistance to edge chipping that is best defined by a fracture toughness in excess of 8 MPamxc2xd, a resistance to chemical attack from the resins included in printed circuit boards and a sharp as possible a cutting edge. Some of these requirements conflict, for instance the high hardness tends to mean a reduced edge toughness. The new products for this application can, therefore, require a reduced WC grain size to produce a higher hardness with reduced toughness. However, if this is combined with an increase in cobalt content an increased toughness can be achieved for the same hardness. This also results in a sharper cutting edge, which is required.
The invention is primarily concerned with the addition of ruthenium to submicron grades of cemented carbide. The levels of addition vary between 5 and 35, preferably between 15 and 30, wt-% of the binder content with the best results obtained at about 25 wt-%. For best effects the cobalt used should be of the fine grain size cobalt powder having deagglomerated spherical grains of about 0.4 xcexcm average grain size and with a narrow grain size distribution. Preferably the cobalt powder is polyol cobalt. The cobalt contents to which this addition can be made should vary from 5-12%, preferably 5-8. The average WC grain size shall be  less than 0.8 xcexcm, preferably  less than 0.4 xcexcm. The cemented carbide of the invention is preferably a straight WC+Co grade but it may also contain  less than 5 wt-% gammaphase.
In order to obtain the submicron WC grain size VC+Cr3C2 is added. Because the Ru also acts as a mild grain growth inhibitor an addition of  less than 0.9 wt % VC+Cr3C2 is generally satisfactory. Particularly good results are obtained if the VC/Cr3C2 ratio in wt % is 0.2-0.9, preferably 0.4-0.8, most preferably 0.6-0.7. Preferably sintering is performed using gas pressure sintering also referred to as sinter-HIP.
The invention also relates to the use of a cemented carbide with submicron WC grain size and with a binder phase containing 10-30 wt-% Ru as a tool for drilling/routing of printing circuit board materials.
The present invention further relates to a method of making a cemented carbide body comprising one or more hard constituents and a binder phase based on cobalt, nickel and/or iron by powder metallurgical methods milling, pressing and sintering of powders forming hard constituents and binder phase whereby said binder phase contains 10-30 wt-% Ru. At least part of the binderphase powder consists of non agglomerated particles of spheroidal morphology of about 0.4 xcexcm average grain size and with a narrow grain size distribution wherein at least 80% of the particles have sizes in the interval xxc2x10.2 x provided that the interval of variation (that is 0.4 x) is not smaller than 0.1 xcexcm.
The advantages offered by the ruthenium additions are as mentioned a further element of grain growth refinement, an increase in resistance to chemical attack and a strengthening of the binder phase without significantly affecting the edge toughness due to the increase in cobalt content used.